1. Field of the Invention
The present invention relates to a diode device in which both electrodes of two terminals are provide on the same surface, and can be directly connected to a conductive pattern of a circuit substrate without using a lead wire.
2. Description of the Related Art
Face-down bonding is a method for directly attaching integrated circuits to circuit boards such as printed boards and the like without using lead wires, conventionally used in the construction of various types of electronic circuits.
According to this method, electrodes are provided on the same surface of the integrated circuit,which is then turned face down and bonded directly to the circuit board. Since the integrated circuit consequently requires no packaging, the size of the integrated circuit can be scaled-down, lowering costs. For these reasons, face-down bonding is generally used.
However, although this method can be used for integrated circuits, chiefly being provided transistors in it, in which electrodes can be disposed on the same surface, it has not been possible to use face-down bonding in the case of diode devices having only two electrodes, such as, for instance, variable-capacity diodes.
FIG. 4 is a cross-sectional view illustrating a conventional variable-capacity diode device, in which region 1 and region 2, having different conductive types, are provided within an epitaxial layer 5 on a silicon semiconductor substrate 3, thereby forming a PN junction such as super abrupt junction.
A first region 1 is exposed at the top face of a semiconductor base, comprising a substrate 3 and an epitaxial layer 5, and therefore an electrode 7 can be provided on the top face thereof. However, since a second region 2 is provided below the first region 1, an electrode 18 of the second region 2 is provided on the bottom face of the substrate 3.
The electrode 18 on the bottom face is attached to a terminal 16. A ribbon-like metal is inserted between the substrate 3 and the terminal 16 at the attach portion and heated, forming a eutectic of the terminal 16, the metal, and the substrate 3.
A metal lead wire 15 connects the electrode 7 on the top face to a terminal 17. Then, with only the terminals 16 and 17 exposed to the outside, a packaging of resin sealant or the like is applied, and the terminals 16 and 17 are connected to a circuit substrate.
Thus it has not been possible to connect the conventional diode device to a circuit board by means of face-down bonding since the two electrodes cannot be provided on the same surface.
The present applicant disclosed an invention to improve the defects of conventional diode devices in Japanese Patent Application Laid-Open No. 9-79112.
However, this technique is not satisfied from an economic view point because it requires a diffusion process.